U.S. Pat. No. 4,523,248 discloses a professional camera system comprising a TV studio camera connected to an accompanying base station by means of a cable (usually a triaxial cable, commonly known as triax) wherein at least two conductors are used for AC power supply. A safety circuit is serially connected between an AC supply and a conductor of the supply cable. The disclosed safety circuit cannot works with a DC supply.
With the introduction of portable triax cameras, the principle was extended with the possibility of supplying such a portable camera with a DC voltage, with the result that the supply in the portable camera itself becomes substantially simpler, more compact, and lighter than with the use of an AC supply with the accompanying transformer or coil which is necessary for protection. According to the safety standard IEC65 valid at the time, a DC voltage of 100 VDC was regarded as safe, and the supply voltage was chosen such that this value was not exceeded. As a result, no safeguard against touching is necessary at this supply voltage when the connection cable is detached.
The standard EN60065 valid at this moment will be changed on Jan. 05, 2001, such that the safe voltage of at most 100 VDC is reduced to at most 60 VDC. This voltage of 60 VDC is too low for transmitting the required power, so that problems will occasionally arise during detaching of the cable.